Flexibility and Constraints of Lepilemur Ecology

Abstract

Using Lepilemur mustelinus as an example of the folivorous guild of lemurs, I address the questions of how potential interspecific competition with Avahi laniger and declining habitat suitability affect its leaf selection and habitat utilization, respectively. The quality of leaves eaten by Lepilemur has been measured in four different forests of Madagascar. Leaf quality was expressed as the ratio of protein to fiber content. In forests where Avahi was absent Lepilemur ate high quality leaves. Where Avahi was present Lepilemur fed on low quality leaves which were inferior to the items eaten by Avahi. Unidentified site effects had no effect on leaf choice of Lepilemur, once the effect of Avahi had been accounted for. This pattern can be considered as behavioral character displacement. Microhabitats used by Lepilemur mustelinus ruficaudatus are characterized by dense stands of trees, interpreted as a prerequisite for locomotion. Up to a certain point Lepilemur tolerates thinning of trees in the wake of logging and uses microhabitats with greater distances between trees. But tree distances in microhabitats used by Lepilemur remain constant when average tree distances are further increased by more intensive forms of logging. This indicates an upper limit due to energetic constraints for distances between trees needed for travel by Lepilemur. Clumping in the distribution of food trees increases with increasing group size from the solitary Lepilemur to the pair-living Avahi to the group-living Propithecus verreauxi. All three results are predicted by deterministic models of optimization theory. This suggests that leaf quality and habitat structure are limiting resources for Lepilemur and that interspecific competition over high quality leaves is an active force in the folivorous guild of Malagasy lemurs.